Refactor valuation marks out of economics

[tradingexpert]

Summary

• Move valuation mark types and compact mark iteration into ordersim.valuation.
• Keep top-level and ordersim.economics imports stable for existing users.
• Align architecture, schema, economics docs, and agent module map with the new boundary.
• Split valuation-specific tests out of economics tests.

Verification

• python -m ruff check .
• python -m pytest — 142 passed, total coverage 98.29%; ordersim.valuation 100%.
• mkdir -p build/cpp && c++ -std=c++17 -Wall -Wextra -pedantic -Icpp cpp/tests/matching_engine_core_test.cpp -o build/cpp/matching_engine_core_test && build/cpp/matching_engine_core_test